Updated pretty printing (#658)
Updated pretty printing (#658)

This commit brings the pretty printer up to date on the following
concepts:

* Using `val`/`var` to introduce variables
* Calling/declaring polymorphic functions
* Implementing traits in classes
* Embedding arbitrary Encore code in embedded C

Since this only changes the code printed in error messages, I have not
created any tests for it.
parapluu/encore,parapluu/encore,parapluu/encore